Methods for Efficient Bandwidth Scaling of Compressed Video Data

Abstract

The present invention relates to systems and methods for efficient bit rate alteration of a bitstream to match an available channel capacity. The efficient bit rate alteration includes selective re-quantization of the compressed bitstream. Selective re-quantization according to the present invention applies multiple re-quantization schemes to different portions of a bitstream. In one embodiment, the multiple re-quantization schemes each have a different computational load. By selectively choosing which type of re-quantization is performed on each portion, efficient bandwidth scaling and data transmission may be achieved both when computational capacity is limited and when video data integrity is important.

1 . A method for converting the bit rate of a compressed bitstream to use an available bandwidth of a channel, the method comprising: selectively re-quantizing a portion of the bitstream according to one of two re-quantization schemes, the first re-quantization scheme comprising variable length decoding the portion, inverse quantizing the portion, re-quantizing the portion with a different quantization step size and variable length encoding the portion, the second re-quantization scheme comprising motion compensated re-quantization of the portion. 
   
   
       2 . The method of  claim 1 , wherein the portion is a frame of the compressed bitstream. 
   
   
       3 . The method of  claim 2 , wherein the frame is re-quantized using the first re-quantization scheme when the frame is a B frame and the frame is re-quantized using the second re-quantization scheme when the frame is a P frame. 
   
   
       4 . The method of  claim 2 , wherein the frame is re-quantized using the first re-quantization scheme when the frame includes chroma information and the frame is re-quantized using the second re-quantization scheme when includes luma information. 
   
   
       5 . The method of  claim 1 , further including performing motion estimation to produce motion vectors for the motion compensated re-quantization. 
   
   
       6 . A network device for providing compressed video data onto a network, the network device comprising: a re-quantization apparatus that receives a compressed video bitstream having a first bit rate and outputs the compressed video bitstream having a second bit rate, the re-quantization apparatus including a first portion configured to receive a first portion of the compressed video bitstream and output the first portion after re-quantization by a first re-quantization scheme, the re-quantization apparatus including a second portion configured to receive a second portion of the compressed video bitstream and output the second portion after re-quantization by a second re-quantization scheme; and a transmitter configured to transmit the compressed video bitstream having the second bit rate onto the network. 
   
   
       7 . The network device of  claim 6 , further including a network interface configured to receive the compressed video bitstream having the first bit rate from the network. 
   
   
       8 . The network device of  claim 6 , further including a rate controller coupled to the re-quantization apparatus. 
   
   
       9 . The network device of  claim 6 , wherein the first portion of the re-quantization apparatus is included in the second portion of the re-quantization apparatus. 
   
   
       10 . The network device of  claim 6 , further including a processor whose processing load at least partially determines which of the first portion and the second portion of the re-quantization apparatus is used.